Y2012-01 Accident at an excavation site in Espoo on 3 July 2012
At 11.52 am on Tuesday 3 July 2012 an accident occurred at a construction site in Matinkylä, Espoo, in which rocks flew into residential buildings, public spaces and the nearby environment, to a distance of 250 metres, due to an excavation blast.
Seven people were injured in the accident, two of them seriously. 30 vehicles and machines were damaged, as were six buildings. A total of 44 injured parties suffered property damage.
Due to the contractor's shortage of resources, the construction site's excavation contract was running late. The contractor hired a new charger, who was on his second working day on the day of the accident. This charger had to handle the blasts himself, because the supervisor in charge of earlier blasting work was on another site.
On the morning of the accident, the charger blasted two fields without difficulties. The next field was larger than these two. After laying the explosives, the field was covered with rubber mats, the danger zone was cordoned off, guards were put into position and the appropriate sound signal was given. The charger blasted the field. Rubber mats rose into the air and a large number of rocks were hurled around uncontrollably.
The explosion which caused the accident occurred because working practices at the excavation site were risky and against requirements and good working practices. No intervention was made in excavation working practices by the excavation and construction work orderer's own supervisory function. Official supervision was unable to prevent the accident. The authority in charge of checking the charger´s certificate was not able, due to current regulations, intervene quickly enough to the charger´s offences.
The unusually powerful explosion and burst of rocks were probably a consequence of a large specific charge (overcharge) somewhere in the field, inadequate covering of the field's front edge (rock cut), or a protrusion left at the front of the rock cut by the preceding explosion. The cause ofthe overcharge may have been a charging error by the charger, incorrect assessment of the burden of the foremost drill holes, the fragmented nature of the rock face, the curving of the drill holes or their combination.
The Safety Investigation Authority gives five recommendations for the improvement of safety in the future. Actors in the construction and excavation sector should develop and implement effective self-supervision practices in the spirit of the regulations in force. Authorities in charge of certificates of proficiency for chargers should draw up improved criteria for assessing the suitability of certificate applicants and holders. The notification and supervision methods employed by the police should be improved. The police should be given the right to suspend a charger's certificate of proficiency. Registers related to blasting work should be simplified, by combining the national ADR certificate with the chargers' certificate of proficiency.